Shinjiro Yagyu

Measurement of bias voltage dependence of local barrier height at constant tip-sample separation

Abstract We measured the bias voltage dependence of the apparent local barrier height (LBH) by STM on an Au (1xa01xa01) surface with an Au tip. The results under two different conditions, a constant tip-sample separation and a constant current, were compared in the low bias voltage range (−30 to −5 mV). Under constant separation, the LBH does not change with the bias voltage, indicating that the LBH is independent of the bias voltage. Under constant current, the LBH increases with increasing absolute value of the bias voltage due to the increase of the tip-sample separation with increasing absolute bias voltage. We found that the LBH depends only on the separation in the low bias voltage range.

Determination of Threshold of Photoelectron Yield Spectroscopy (PYS) Using Machine Learning

In order to analyze the threshold of photoelectron yield spectroscopy (PYS) automatically, we compared the accuracy of the analysis between a fitting (least squares method) method and a machine learning method. Both methods are comparable in terms of the performance of analysis, but machine learning shows better performance in data with high noise components. In the analysis of measured Au data, machine learning shows close to the analyzed value by an analyst, but the fitting method shows the different value due to the influence of a high signal intensity.

Transport properties of single-component organic conductors, TED derivatives

Narrow-gap semiconductors with high conductivity and mobility are an important class of materials for various applications, especially for thermoelectric and optical device applications. Herein, we designed and synthesized novel organic narrow-gap semiconductors, which are modified forms of the main skeleton of a single-component pure organic metal, tetrathiafulvalene-extended dicarboxylate (TED). Molecular design of the TED derivatives with substituent groups on the skeleton led to highly-conducting semiconductors even when powder crystalline samples were used. Their thermopower is greater than that of metallic TED without a substituent group, demonstrating the successful tuning of carrier concentration in the TED system by molecular design. Near-/middle-infrared (IR) diffuse reflectance measurements revealed each band gap, and optical parameters extracted from the spectra evaluated the carrier concentration and mobility of the TED derivatives with fitting calculations on the basis of a Drude–Lorentz dielectric function.